The present invention relates to a technology for implementing a recording/readback device and a recording/readback circuit for performing high-density data storage.
In high-density data recording/readback devices that use magnetic/optical media signal processing systems are required to perform recording/readback operations including: converting data to be recorded into a signal and recording the signal to a medium; and decoding signal information read from a recording medium into data with a high degree of reliability. In particular, with recording media on which information is stored at high recording densities, the readback signals show significantly degraded signal quality. This results from factors such as low signal levels due to smaller storage units, deformations in waveforms due to intersymbol interference, disturbances due to electrical noise or physical defects on media and problems between the media and the readback transducer (head).
To overcome this type of readback signal degradation, and in particular to improve reliability in the decoding of recorded data with regard to increased intersymbol interference and noise, there has recently been active use of high-level data transfer communication technologies such as the PRML (Partial-Response Maximum-Likelihood) method, which is based on digital signal processing technology. Recording/readback signal processing technologies that make use of these techniques are implemented in integrated circuits and the like and are used widely in magnetic disk devices and the like. Much of this technology comes from data decoding technology based on maximum-likelihood sequence estimation, which is implemented using the Viterbi algorithm, and a readback waveform equalization technology based on partial-response technology. The former provides tolerance for increased intersymbol interference in the readback signal while the latter reduces random decoding errors that accompany the decoding of data with high levels of noise. These work to compensate for decreased reliability in the decoded data.
Also, conventional technologies generally use error correction coding technologies. The reliability of decoded data is improved by performing detection and correction of errors during readback for decoding errors generated after decoding data using the maximum-likelihood technique described above. An example of this error correction coding (ECC) technology is the combination error correction coding technology that uses the interleaving technique and Reed-Solomon coding. This is used in many information storage devices, including magnetic disk devices and optical disk devices. Thus, it is possible to detect and correct errors in the decoded data generated from the various factors described above including random decoding errors caused during data decoding by noise. This allows a high degree of reliability to be maintained in the decoding and readback of data stored in high-density storage/readback devices. Implementations of this type of error correction coding technology can be found, for example, in R. D. Cydecyan, “A PRML system for Digital Magnetic Recording” (IEEE Journal on Selected Areas in Communications, Vol.10, No.1, 1992) as well as in Japanese Laid-open Patent Publication number 11-168514 (U.S. application Ser. No. 09/124,840). For increasing storage density in information recording/readback devices and improving reliability in data decoding and readback, the main technologies are PRML signal processing, which provides a data decoding technique based on the maximum likelihood sequence estimation referred to above, and error detection/correction coding.